1. Field
The present disclosure generally relates to air intake ducting of supersonic propulsion systems and, in particular, to cooling of the engine air intakes of hypersonic vehicles.
2. Description of the Related Art
The air intakes of high-speed vehicles benefit from removal of the boundary layer in order to achieve higher thrust. One conventional approach to boundary layer removal uses an intake “bleed” system in the inlet surface which allows the boundary layer to flow though the surface and be collected into a plenum. This bleed air is then ducted overboard. At very high speeds, the stagnant bleed air in the plenum becomes very hot as the kinetic energy of the high-speed air is converted to heat as the air is slowed within the plenum. At speeds above Mach 4, these temperatures may exceed the temperature limit of most materials. As a result, conventional high-speed intake systems do not include bleed systems.
Vehicles using air-breathing engines that initially fly at subsonic speeds and then accelerate to supersonic flight speeds must use air intakes that can accept the supersonic shock wave that enters the air intake during the transition from subsonic to supersonic flight. Allowing the shock wave to travel from the inlet aperture to the intake throat is referred to as “swallowing” the supersonic flow and is necessary to “start” supersonic operation. To accomplish the “starting” process requires a relatively large amount of air to be bled off of the air intake during the subsonic flow. As allowing this same amount of air to bleed off during supersonic flow reduces the efficiency of the engine, active bleed control systems, referred to as “educated bleed slots,” are used in conventional systems to adjust the amount of air that is bleeding off of the air intake. The disadvantage of active bleed control systems is the increased complexity and weight and reduction in reliability that are inherent in adding moving elements and actuators to a system.